The present invention relates to a device for spraying coating product comprising a rotating spray element, such as a bowl or dish, driven in rotation at high speed by drive means such as a rotor of an air turbine. The invention also relates to a rotating spray element that may be used with this device.
In an installation for spraying liquid or particulate coating product, it is known to spray the product by means of a bowl or a dish supplied with product and rotating at a speed of the order of 30,000 rpm. At such a speed of rotation, it is desirable that the bowl or dish be as light as possible and balanced, in order to avoid unbalance to a maximum, particularly if the drive turbine is an air-bearing and/or magnetic turbine.
It is known to assemble a rotating spray element on the rotor of a turbine by means of a threaded rod extending axially with respect to the rotor and by means of an axial tapping of the rotating element or bowl, or by bolts distributed circumferentially about the axis of rotation of this element. Such a type of assembly considerably increases the weight of the rotating assembly while the operations of assembly and dismantling are long and fastidious, which is not forcibly compatible with the times available for maintenance, particularly on an automobile vehicle production chain.
WO-A-94/12286 discloses a spraying device comprising a bowl connected to the rotor of a spray thanks to a radially expansible fitting crown. This system is satisfactory.
U.S. Pat. No. 4,473,188 discloses spreading equipment comprising a rotating nozzle driven by an electric motor. The coupling between this nozzle and the driven shaft of the motor is effected by abutment of a metal ring fast with the nozzle on a magnet driven by this shaft. Such surface abutment pre-supposes a precise positioning of the nozzle with respect to the shaft, which limits the speed of rotation of the nozzle. In addition, if metal particles are deposited on the magnet, the surface abutment of the ring is no longer possible, which hinders the coupling between the nozzle and the shaft of the motor. Moreover, the successive positionings of nozzles on the shaft may damage that surface of the magnet intended to receive the rings of the nozzles in abutment. This device is therefore not adapted for the spraying of coating product for which the bowl must be regularly cleaned and/or changed, with subsequent re-positioning of this bowl or a fresh bowl.
It is an object of the invention to propose an alternative solution to the one disclosed in WO-A-94/12286, which is particularly simple from the structural standpoint, therefore reliable and of attractive cost price, and compatible with the spraying of coating product.
To that end, the invention relates to a device for spraying coating product of the type mentioned above, which comprises means for magnetic coupling between the rotating spray element and the drive means associated therewith, and which is characterized in that an air-gap is formed between these magnetic coupling means.
Thanks to the use of magnetic coupling means, assembly and dismantling of the rotating spray element on and from its drive means are particularly rapid, since it suffices to bring the rotating element sufficiently close to the drive means for the magnetic coupling to produce an efficient effect of connection. These coupling means also allow a magnetic centering of the rotating element with respect to the rotor. As an air-gap is formed between the magnetic coupling means, there is no risk of upsetting the opposite surfaces of the coupling means, even after the bowl has been positioned several times. Moreover, a possible deposit of metal particles or of impurities on one of these opposite surfaces does not hinder operation of the couplig means. Particular precautions are therefore unnecessary for positioning a bowl.
According to a first embodiment of the invention, the rotating element is equipped with at least one magnet adapted to cooperate with a magnetic looping element borne by the drive means.
According to another advantageous embodiment of the invention, the drive means are equipped with at least one magnet adapted to cooperate with a magnetic looping element borne by the rotating element.
According to a third embodiment of the invention, the rotating element and the rotor are each provided with a magnet, the polarities of these magnets being oriented so that a force of attraction is generated between these magnets when the rotating element is mounted on the rotor.
Whatever the embodiment considered, the permanent magnet may be in the form of an annulus or a sector of annulus centred on the axis of rotation of the rotating element. In a variant embodiment, a plurality of magnets in the form of sectors of annulus or of studs are distributed about the axis of rotation. Similarly, the looping element may be a metal annulus centred on the axis of rotation of the rotating element.
According to another advantageous aspect of the invention, the magnet and/or the looping element is force-fitted in a housing made in the rotating element or in the drive means.
According to another advantageous aspect of the invention, the device comprises mechanical means for centering the rotating spray element with respect to the drive means. These centering means allow a pre-positioning of the magnetic coupling means during positioning of the spray element on the drive means. These centering means also contribute to the correct hold of the spray element on its drive means. In that case, the rotating element may be provided to comprise at least one truncated surface bearing against a corresponding truncated surface of the drive means. A truncated surface of the rotating element is advantageously formed substantially around the magnetic coupling means. In addition, a truncated surface of the drive means may be provided to be formed at the level of a free edge of a skirt defining a volume for partially receiving the rotating element.
According to another advantageous aspect of the invention, the magnetic coupling means also constitute means for self-centering the rotating element on the rotor, which makes it possible to envisage total or partial elimination of the mechanical centering means.
The invention also relates to a rotating spray element or bowl capable of being used with a device as described hereinbefore and which bears means adapted to cooperate with complementary means provided on a drive member for connecting the bowl and the member in question by magnetic coupling, while the bowl is provided with a bearing surface against a corresponding surface of this member in such a position that an air-gap is formed between the above-mentioned magnetic coupling means which cooperate.